Generically, a user's computer in a remote location.
Specifically, a feature in high-end versions of Windows (XP Pro, Vista Business, Win7 Pro, etc.) that allows the machine to be run remotely from another Windows machine over any dial-up or TCP/IP connection (LAN or Internet). Also called "Remote Desktop Connection," it uses the Remote Desktop Protocol (RDP) to exchange only keystrokes, mouse movement and screen changes. See remote control software
and Remote Desktop Services